Effects of a Subgrid-Scale Topography and Land Use Scheme on the Simulation of Surface Climate and Hydrology. Part I: Effects of Temperature and Water Vapor Disaggregation

Abstract

A mosaic-type parameterization of subgrid-scale topography and land use is implemented within the framework of a regional climate model, and its effects on a multiseasonal simulation over the European region are tested, with focus on the Alpine subregion. The parameterization adopts a regular finescale surface subgrid for each coarse model grid cell. Meteorological variables are disaggregated from the coarse grid to the fine grid, land surface calculations are then performed separately for each subgrid cell, and surface fluxes are reaggregated onto the coarse grid cell for input to the atmospheric model. The primary effects of the subgrid surface scheme are 1) an improvement of the finescale structure and overall simulation of surface air temperature over complex terrain, and 2) a more realistic simulation of snow as driven by the complex terrain features. The subgrid scheme also affects the warm season simulation through feedbacks between precipitation and the surface hydrology. The primary aspect of the scheme that has an impact on the model is the subgrid disaggregation of temperature and water vapor, which is based on the difference between the topographical elevation of the subgrid and corresponding coarse grid cells. The mosaic-type approach presented here with suitable meteorological disaggregation techniques and with the possible addition of a parameterization of subgrid-scale effects on precipitation can provide an effective tool to bridge the scaling gap between climate models and surface hydrological processes.